Deposition of smooth metal nitride films

ABSTRACT

In one aspect, methods of forming smooth ternary metal nitride films, such as Ti x W y N z  films, are provided. In some embodiments, the films are formed by an ALD process comprising multiple super-cycles, each super-cycle comprising two deposition sub-cycles. In one sub-cycle a metal nitride, such as TiN is deposited, for example from TiCl 4  and NH 3 , and in the other sub-cycle an elemental metal, such as W, is deposited, for example from WF 6  and Si 2 H 6 . The ratio of the numbers of each sub-cycle carried out within each super-cycle can be selected to achieve a film of the desired composition and having desired properties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of semiconductor devicemanufacturing and, more particularly, to methods for forming metalnitride films by a combination of atomic layer deposition (ALD)processes for depositing metal nitride and elemental metal. For example,smooth Ti_(x)W_(y)N_(z) films may be formed by utilizing atomic layerdeposition processes for depositing TiN and W.

2. Description of the Related Art

Atomic layer deposition (ALD) is based on sequential, self-saturatingsurface reactions, which can provide good conformality and step coverageregardless of the geometry of the structure to be coated. However,deposition of metallic films by ALD has been challenging, in partbecause ALD is based essentially on thermodynamically favorablehalf-reactions. Apart from the noble metals, elements in their pureforms are not the thermodynamically most stable forms of the elementsbut rather their compounds. Therefore, the choice of precursors fordepositing metallic films by ALD has been a challenging task.

Metallic compound films such as nitrides and carbides are easier todeposit by ALD compared to pure elemental films. However, thethermodynamic stability of these films is typically also substantiallylower than their corresponding metal oxides and the same difficulty inthe precursor chemistry choice arises as with the elemental films.

Refractory metal conducting layers are basic building blocks in microand nano-electronics. Titanium nitride and tungsten layers are commonlyused in the semiconductor manufacturing industry. Titanium nitride isused, for example, as a gate electrode material or as a copper diffusionbarrier. Tungsten is mainly used as the contact plug material in metal 1level interconnects. Both materials can be deposited by physical vapordeposition (PVD), by chemical vapor deposition (CVD) or by ALD methods.For ultra-high aspect ratio structures found in the current state of theart microelectronic chips and in future nodes, ALD deposition methodsare preferred because they are capable of providing better conformalityand step coverage.

In addition to the electrical properties of the metal films, such asresistivity and work function, one of the most important properties ofthe films is their microstructure. Metallic films favor apolycrystalline phase, often having specific grain morphology. Duringthe deposition process, many metals adopt columnar grain morphology witha certain preferred crystal orientation relative to the substrate. Thegrain boundaries between the columnar grains present discontinuities inthe material, which alter the mechanical and electrical properties ofthe films and may serve as diffusion channels for impurities. As aresult, the desired material properties are degraded compared to theiramorphous or single crystal phases. In the case of nanocrystallinealloys however, the grain boundaries may also have a positive effect onthe material properties, namely by thermodynamically stabilizing thenanocrystalline phase of the alloy through the segregation of theelemental distributions of the alloy elements between the grainboundaries and the bulk of the grains.

SUMMARY OF THE INVENTION

In one aspect, atomic layer deposition (ALD) processes are provided fordepositing metal nitride thin films. In some embodiments the ALDprocesses may comprise a plurality of super-cycles, where at least onesuper-cycle comprises two sub-cycles: a first sub-cycle for formingmetal nitride and a second sub-cycle for forming elemental metal. Thesub-cycles are repeated a predetermined number of times and at apredetermined ratio in one or more super-cycles to deposit a metalnitride film of the desired composition and thickness.

In some embodiments, a ternary metal nitride film comprising twodifferent metals, M¹ and M², is deposited on a substrate in a reactionchamber by an atomic layer deposition process comprising a plurality ofsuper-cycles, where a super-cycle comprises a metal nitride sub-cycleand an elemental metal sub-cycle.

In some embodiments the metal nitride sub-cycle comprises pulsing afirst vapor-phase metal precursor comprising a first metal M¹ into thereaction chamber. In some embodiments at most a molecular layer of thefirst metal precursor is formed on the substrate. A vapor phase nitrogenprecursor is subsequently pulsed into the reaction chamber where itreacts with the first metal precursor on the substrate to form a metalnitride. In some embodiments M¹ is selected from Ti, Ta, Nb, Mo, and W.The first metal precursor may comprise, for example, a metal halide ormetal-organic compound. In some embodiments the nitrogen reactant maycomprise ammonia, N₂H₄, nitrogen atoms, nitrogen containing plasma ornitrogen radicals.

In some embodiments the elemental metal sub-cycle comprises pulsing asecond vapor phase metal precursor comprising a second, different metalM² into the reaction chamber. In some embodiments at most a molecularmonolayer of second metal precursor is formed on the substrate. A vaporphase second reactant is pulsed into the reaction chamber where itreacts with the second metal precursor to form elemental metal. Thesecond reactant may comprise, for example, a silane or borane, such asdisilane or trisilane.

In another aspect, ALD processes for depositing a ternary metal nitridefilm on a substrate are provided, where the ALD processes may comprise aplurality of deposition super-cycles. One or more of the super-cyclescomprises a TiN deposition sub-cycle and a W deposition sub-cycle. Thesub-cycles are repeated a predetermined number of times and at apredetermined ratio in one or more super-cycles to deposit a metalnitride film of the desired composition and thickness.

In some embodiments the TiN deposition sub-cycle comprises alternatelyand sequentially contacting the substrate with a titanium precursor anda nitrogen reactant. In some embodiments the titanium precursor is atitanium halide or metal-organic titanium compound. For example, thetitanium precursor may be TiCl₄. The nitrogen reactant may, for example,be selected from the group consisting of ammonia, N₂H₄, nitrogen atoms,nitrogen containing plasma and nitrogen radicals.

In some embodiments the W deposition sub-cycle comprises alternately andsequentially contacting the substrate with a tungsten precursor and asecond precursor, where the second precursor is a silane or borane. Insome embodiments the tungsten precursor is a tungsten halide or metalorganic tungsten compound. For example, the tungsten precursor may beWF₆. The second precursor may comprise, for example, silane or disilane.

In some embodiments the TiN deposition sub-cycle and the W sub-cycle arecarried out at a ratio of at least about 3 in at least one of theplurality of super-cycles.

In some embodiments the metal nitride layer forms a continuous layer. Insome embodiments the metal nitride layer is not a nanolaminate.

In another aspect, methods for forming ternary metal nitride films on asubstrate in a reaction chamber may comprise a first metal nitridesub-cycle and a second elemental metal sub-cycle, where the metalnitride sub-cycle and the elemental metal sub-cycle are repeated to formthe ternary metal nitride film at a desired thickness.

In some embodiments the first metal nitride sub-cycle may comprisecontacting the substrate with a vapor phase first metal precursor and anitrogen reactant. The second elemental metal sub-cycle may comprisecontacting the substrate with a vapor phase second metal precursor and asecond reactant. The metal in the first metal precursor may be differentfrom the metal in the second metal precursor. In some embodiments theelemental metal sub-cycle is performed before the metal nitridesub-cycle.

In some embodiments the first metal nitride sub-cycle and the secondelemental metal sub-cycle are performed at a selected ratio in one ormore super-cycles. In addition, the number of sub-cycles may be limitedin each super-cycle. For example, the first sub-cycle may be repeated nomore than about 40 times consecutively prior to the second sub-cycle insome embodiments. In some embodiments the second sub-cycle is performedno more than about 10 times consecutively in each of the plurality ofsuper-cycles.

In some embodiments a ternary metal nitride film is deposited that has aroughness of less than about 2 nm at a thickness of about 20 to about 50nm, as measured by x-ray reflectivity (XRR).

In some embodiments the ratio of sub-cycles is selected such that thefilm is electrically continuous i.e. conducts current at very thinthicknesses, such as less than about 3 nm, less than about 2 nm, lessthan about 1.5 nm or even less than about 1.0 nm

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the detailed descriptionand from the appended drawings, which are meant to illustrate and not tolimit the invention, and wherein:

FIG. 1 is a flow chart illustrating an ALD process for depositing aTi_(x)W_(y)N_(z) film according to one embodiment.

FIGS. 2A-C show XRD patterns of 100 cycles of pure ALD-W films depositedon TiN (FIG. 2A), SiO₂ (FIG. 2B) and HfO₂ (FIG. 2C) surfaces.

FIGS. 3A and B show XRD patterns of Ti_(x)W_(y)N_(z) films depositedusing different TiN/W cycle ratios.

FIG. 4 shows a comparison of the morphology of W_(x)N_(y) andTi_(x)W_(y)N_(z) layers deposited with various ratios of TiN to Wdeposition cycles, as well as pure W and TiN.

FIG. 5 shows SEM images of a W_(0.9)N_(0.1) (TiN/W cycle ratio=1) filmdeposited in a 3D trench structure. The grain size was too small to bedetected with SEM. The conformality and step coverage of the filmappears to be excellent.

FIGS. 6A and B show heated stage XRD patterns of aTi_(0.26)W_(0.33)N_(0.41) (20:1 TiN/W cycle ratio) film in nitrogenatmosphere. No signs of grain coarsening with heating up to 875° C. areseen. FIG. 6B shows a comparison with a pure TiN film having a similarthickness.

FIGS. 7A and B show heated stage XRD patterns of aTi_(0.26)W_(0.33)N_(0.41) (20:1 TiN/W cycle ratio) film in airatmosphere.

FIGS. 8A and B illustrate (Ti+W)/(Si+Ti+W) or layer closure as afunction of estimated layer thickness. FIG. 8B is an expanded view ofFIG. 8A.

FIGS. 9A and B show Ti/(Ti+W) as a function of estimated layerthickness. FIG. 9B is an expanded view of FIG. 9A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As mentioned above, metal nitride, such as titanium nitride, andelemental metal, such as tungsten, are commonly used in thesemiconductor industry, for example as gate metals, contact plugs andMIM electrodes. The present application is based, in part, on theunexpected finding that two ALD processes, one for depositing a metalnitride and one for depositing elemental metal, can be used together toproduce a metal nitride film. In some embodiments one ALD process fordepositing TiN and one for depositing W can be used together to producea metal nitride film, such as a Ti_(x)W_(y)N_(z) film. The film may haveadvantageous properties relative to known TiN or W films. Each processalone produces films with significant roughness and a columnar grainstructure, which are undesirable properties for many electronicapplications. For example, for copper barrier applications a columnargrain structure can allow copper to diffuse through grain boundaries.However a combination of the processes, as described herein, can be usedto produce films with improved properties.

As described in more detail below, by mixing two ALD processes fordepositing metal nitride and elemental metal, for example for depositingTiN and W, metal nitride films, such as Ti_(x)W_(y)N_(z) films, can beformed. The films may have improved properties relative to the TiNand/or W films deposited individually or other similar metal nitrides.In particular, in some embodiments smooth, conductive films where thecolumnar structure is reduced or absent can be formed. In addition,continuous ultra-thin films, for example less than 3 nm, can bedeposited. Moreover, by adjusting the ratio of the two processes,various physical properties of the films can be adjusted, such as theresistivity and mechanical properties such as density. In someembodiments, a solid solution of nanocrystalline TiN and W₂N is formedusing processes for depositing TiN and W.

The ALD processes described below can be used to deposit metal nitridefilms, which can be referred to as M¹M²N films, where M¹ and M² aredifferent metals, such as TiWN. The stoichiometry, and thus the relativeamounts of M¹, M² and N, can vary. For example, the relative amounts ofTi, W and N in a TiWN film can vary. Thus, the films are referred toherein primarily as M¹ _(x)M² _(y)N_(z) films, for exampleTi_(x)W_(y)N_(z) films. The variables x, y and z will vary depending onthe particular deposition process and conditions. In some embodiments xis from about 0, or just above, to about 1.5, y is from about 0.05 toabout 4 and z is from about 0, or just above, to about 2 In someembodiments the stoichiometry is near the range of the stoichiometry ofa solid solution of TiN and W₂N. In some embodiments x is from about 0,or just above, to about 1, y is from about 0.1 to about 1 and z is fromabout 0, or just above, to about 0.8. In some embodiments x is fromabout 0, or just above, to about 0.5, y is from about 0.3 to about 0.95and z is from about 0.05 to about 0.5 The amount of each element in thefilm can be controlled, for example by controlling the ratio of themetal nitride to elemental metal deposition cycles.

In some embodiments in which a Ti_(x)W_(y)N_(z) film is deposited, theamount of titanium, nitrogen and tungsten in the films can be controlledby controlling the ratio of TiN and W deposition sub-cycles, asdescribed in detail below. For example, if the TiN:W sub-cycle ratio isless than or equal to about 1, W_(y)N_(z) films with a nitrogen contentof less than about 10 at.-% can be produced. These films do not comprisean appreciable amount of titanium (x≈0). With TiN/W cycle rations higherthan about 3, thin films comprising ternary Ti_(x)W_(y)N_(z) solidsolutions are formed. The variable z will not be zero for a ternaryfilm, but if the TiN:W pulsing ratio is 0, the resulting film will bepure tungsten and z will be zero. The titanium content increases lessthan the nitrogen content with an increasing TiN/W cycle ratio. Withoutbeing bound to any theory, it is believed that in some circumstances asolid solution may be formed, leading to a phenomenon called solidsolution strengthening.

In some embodiments, methods of forming aM¹ _(x)M² _(y)N_(z) filmcomprise a first ALD sub-cycle in which metal nitride is deposited byalternately and sequentially contacting a substrate with a metalprecursor, such as a metal halide, and a nitrogen reactant, such as NH₃,and a second ALD sub-cycle in which elemental metal is deposited byalternately and sequentially contacting the substrate with a metalreactant, such as a metal halide and a second reactant, such as Si₂H₆.The two sub-cycles together form a super-cycle that can be repeated asmany times as desired to achieve a film of an appropriate thickness fora particular application. Within each super-cycle, the ratio of metalnitride to metal sub-cycles can be adjusted to achieve a desired filmcomposition and properties.

In some embodiments, methods of forming a Ti_(x)W_(y)N_(z) film comprisea first ALD sub-cycle in which titanium nitride is deposited byalternately and sequentially contacting a substrate with a titaniumprecursor, such as TiCl₄ and a nitrogen reactant, such as NH₃, and asecond ALD sub-cycle in which tungsten is deposited by alternately andsequentially contacting the substrate with a tungsten reactant, such asWF₆ and a second reactant, such as Si₂H₆. The two sub-cycles togetherform a super-cycle that can be repeated as many times as desired toachieve a film of an appropriate thickness for a particular application.Within each super-cycle, the ratio of TiN to W sub-cycles can beadjusted to achieve a desired film composition and properties.

In some embodiments the M¹ _(x)M² _(y)N_(z) film is not a nanolaminateand separate layers of metal nitride and elemental metal are notvisible. In some embodiments less than about 60 or less than about 40consecutive metal nitride deposition sub-cycles (M¹ _(x)N_(z)) arecarried out in a super-cycle. In some embodiments less than about 10 orless than about 5 consecutive elemental metal deposition sub-cycles (M²_(y)) are carried out in a super-cycle.

For example, in some embodiments a Ti_(x)W_(y)N_(z) film is not ananolaminate film or a film in which distinct and separate layers oftungsten and titanium nitride are observable. In some embodiments lessthan about 60 or less than about 40 consecutive TiN depositionsub-cycles are carried out in a super-cycle. In some embodiments lessthan 10 or less than about 5 consecutive W deposition sub-cycles arecarried out in a super-cycle.

The concentration of the first metal, nitrogen and second metal can bevaried to change the properties of the M¹ _(x)M² _(y)N_(z) film. Forexample, the concentration of titanium, nitrogen and tungsten can bevaried to change the properties of a Ti_(x)W_(y)N_(z) film. In someembodiments a Ti_(x)W_(y)N_(z) film comprises a higher concentration oftitanium than tungsten. In some embodiments a Ti_(x)W_(y)N_(z) filmcomprises a higher concentration of tungsten than titanium.

While illustrated primarily in the context of forming Ti_(x)W_(y)N_(z)films, other metal nitride films can be deposited using an ALDsuper-cycle comprising a metal nitride sub-cycle and an elemental metalsub-cycle.

In some embodiments, methods of forming a M¹ _(x)M² _(y)N_(z) filmcomprises a plurality of ALD super-cycles, at least one super-cyclecomprising a sub-cycle for forming M¹ _(x)N_(z), wherein M¹ can beselected from Ti, Ta, Nb, Mo and W, and a sub-cycle for depositingelemental metal M², wherein M² is W or Mo. In the first ALD sub-cycle,M¹ nitride is deposited by alternately and sequentially contacting asubstrate with a precursor containing metal M¹, such as a metal halide,and a nitrogen reactant, such as NH₃. In the second ALD sub-cycleelemental metal M² is deposited by alternately and sequentiallycontacting the substrate with a reactant containing metal M², such as ametal halide and a second reactant, such as silane, like Si₂H₆, orborane, like B₂H₆. The two sub-cycles together form a super-cycle thatcan be repeated as many times as desired to achieve a film of anappropriate thickness for a particular application. Within eachsuper-cycle, the ratio of metal nitride subcycles (M¹ _(x)N_(z)) toelemental metal (M²) sub-cycles can be adjusted to achieve a desiredfilm composition and properties.

In some embodiments the methods of forming M1^(I) _(x)M² _(y)N_(z) film,wherein M¹ can be selected from Ti, Ta, Nb, Mo and W, and M² is W or Mo,comprises combining two ALD processes, where the two individualprocesses are known to produce metal nitride films with columnar grainstructure (M¹ based metal nitride film process) and elemental metalfilms with either columnar grain structure or a rough film (M² basedelemental metal film process). In some embodiments the M¹ _(x)M²_(y)N_(z) film is smooth and does not have columnar grain structure.

The concentration of the M¹, nitrogen and M² can be varied to change theproperties of the M¹ _(x)M² _(y)N_(z) film. In some embodiments the M¹_(x)M² _(y)N_(z) film comprises a higher concentration of M¹ than M². Insome embodiments the M¹ _(x)M² _(y)N_(z) film comprises a higherconcentration of M² than M¹.

Atomic Layer Deposition (ALD)

ALD type processes are based on controlled, self-limiting surfacereactions of precursor chemicals. Gas phase reactions are avoided byfeeding the precursors alternately and sequentially into the reactionchamber. Vapor phase reactants are separated from each other in thereaction chamber, for example, by removing excess reactants and/orreactant by-products from the reaction chamber between reactant pulses.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure. Insome embodiments the substrate comprises a 300 mm silicon wafer. In someembodiments the substrate comprises a 450 mm wafer. Depositiontemperatures are maintained below the precursor thermal decompositiontemperature but at a high enough level to avoid condensation ofreactants and to provide the activation energy for the desired surfacereactions. Of course, the appropriate temperature window for any givenALD reaction will depend upon the surface termination and reactantspecies involved.

A first reactant is conducted into the chamber in the form of vaporphase pulse and contacted with the surface of a substrate. Conditionsare preferably selected such that no more than about one monolayer ofthe precursor is adsorbed on the substrate surface in a self-limitingmanner. Excess first reactant and reaction byproducts, if any, arepurged from the reaction chamber, often with a pulse of inert gas suchas nitrogen or argon.

Purging the reaction chamber means that vapor phase precursors and/orvapor phase byproducts are removed from the reaction chamber such as byevacuating the chamber with a vacuum pump and/or by replacing the gasinside the reactor with an inert gas such as argon or nitrogen. Typicalpurging times are from about 0.05 to 20 seconds, more preferably betweenabout 1 and 10, and still more preferably between about 1 and 2 seconds.However, other purge times can be utilized if necessary, such as whendepositing layers over extremely high aspect ratio structures or otherstructures with complex surface morphology is needed. The appropriatepulsing times can be readily determined by the skilled artisan based onthe particular circumstances.

A second gaseous reactant is pulsed into the chamber where it reactswith the first reactant bound to the surface. Excess second reactant andgaseous by-products of the surface reaction are purged out of thereaction chamber, preferably with the aid of an inert gas. The steps ofpulsing and purging are repeated until a thin film of the desiredthickness has been formed on the substrate, with each cycle leaving nomore than a molecular monolayer. As discussed in detail below, informing M¹ _(x)M² _(y)N_(z) films, such as Ti_(x)W_(y)N_(z) films, twodeposition sub-cycles are repeated one or more times in each ALDsuper-cycle.

Additional reactants can also be supplied that, in some embodiments, donot contribute elements to the growing film. Such reactants can beprovided either in their own pulses or along with precursor pulses, andcan be used for example to provide a desired surface termination, or tostrip or getter adhered ligands and/or free by-product.

As mentioned above, each pulse or phase of each cycle is preferablyself-limiting. An excess of reactant precursors is supplied in eachphase to saturate the susceptible structure surfaces. Surface saturationensures reactant occupation of all available reactive sites (subject,for example, to physical size or “steric hindrance” restraints) and thusprovides excellent step coverage. In some arrangements, the degree ofself-limiting behavior can be adjusted by, e.g., allowing some overlapof reactant pulses to trade off deposition speed (by allowing someCVD-type reactions) against conformality. Ideal ALD conditions withreactants well separated in time and space provide near perfectself-limiting behavior and thus maximum conformality, but sterichindrance results in less than one molecular layer per cycle. LimitedCVD reactions mixed with the self-limiting ALD reactions can raise thedeposition speed.

Examples of suitable reactors that may be used include commerciallyavailable ALD equipment such as the F-120® reactor, Pulsar® reactor andAdvance® 400. Series reactor, available from ASM America, Inc ofPhoenix, Ariz. and ASM Europe B.V., Almere, Netherlands. In addition tothese ALD reactors, many other kinds of reactors capable of ALD growthof thin films, including CVD reactors equipped with appropriateequipment and means for pulsing the precursors can be employed. In someembodiments a flow type ALD reactor is used.

In some embodiments the reactor is batch reactor and has more than about50 substrates, more than about 100 substrates or more than about 125substrates. In some embodiments the reactor is mini-batch reactor andhas from 2 to about 20 substrates, from 3 to about 15 substrates or from4 to about 10 substrates.

The M¹ _(x)M² _(y)N_(z) and Ti_(x)W_(y)N_(z) ALD processes describedbelow can optionally be carried out in a reactor or reaction spaceconnected to a cluster tool. In a cluster tool, because each reactionspace is dedicated to one type of process, the temperature of thereaction space in each module can be kept constant, which improves thethroughput compared to a reactor in which is the substrate is heated upto the process temperature before each run.

A stand-alone reactor can be equipped with a load-lock. In that case, itis not necessary to cool down the reaction space between each run.

M^(I) _(x)M^(III) _(y)N_(z) Film Deposition

As mentioned above and discussed in detail below using TiN and Wsub-cycles r cycles as an example for the formation of aTi_(x)W_(y)N_(z) film, M¹ _(x)M² _(y)N_(z) films can be deposited usinga metal nitride deposition sub-cycle and an elemental metal sub-cycle.In some embodiments M¹ can be selected from Ti, Ta, Nb, Mo and W, and M²is W or Mo. In some embodiments M¹ and M² are not the same metal. Thetwo sub-cycles can be repeated at a desired ratio in a super-cycle toform a smooth and/or nanocrystalline film. In some embodiments the M¹_(x)M² _(y)N_(z) films do not have a columnar grain structure.

In some embodiments the M¹ _(x)M² _(y)N_(z) deposition process is an ALDprocess. In some embodiments the M¹ _(x)M² _(y)N_(z) film depositionprocess is a sequential or cyclic process, such as a sequential orpulsed CVD process utilizing the same precursor and conditionsselections as an ALD process. In some embodiments the M¹ _(x)M²_(y)N_(z) film deposition process has a step which is not self-limiting.In some embodiments the process may operate in a process conditionregime close to CVD conditions or in some cases fully in CVD conditions.

In some embodiment a M¹ _(x)M² _(y)N_(z) film deposition process maycomprise multiple super-cycles, where each super-cycle comprises atleast one M¹ _(x)N_(z) sub-cycle and at least one M² sub-cycle. In someembodiments, each deposition sub-cycle comprises alternately andsequentially contacting the substrate with a metal precursor and secondprecursor. The ratio of the M¹ _(x)N_(z) and M² sub-cycles can be variedto achieve the desired composition, and the number of super-cycles canbe selected to deposit a metal nitride film of the desired thickness.The number of each sub-cycles conducted consecutively in a super-cycleis limited such that a mixed M¹ _(x)M² _(y)N_(z) film is formed, anddistinct M¹ _(x)N_(z) and M² layers are not visible.

The super-cycle can be written as:

a[b(M¹-precursor+N-precursor)+c(second reactant+M²-precursor)], where(M¹-precursor+N-precursor) represents M¹ _(x)N_(z) sub-cycle and b isthe number of M¹ _(x)N_(z) sub-cycles in each super-cycle, (secondreactant+M²-precursor) represents the M² sub-cycle and c is the numberof M² sub-cycles in each super-cycle and a is the number ofsuper-cycles. The ratio of metal nitride to elemental metal cycles canbe given as b:c.

The first and second deposition sub-cycles (b and c) may be provided ata selected ratio to deposit a thin film with a desired composition anddesired properties. For example, in some embodiments the ratio of thefirst, metal nitride deposition sub-cycle to the second elemental metaldeposition sub-cycle in one or more super-cycles may be from about 0.1to about 100, about 0.25 to about 50 or about 0.5 to about 40. In someembodiments the ratio of metal nitride deposition sub-cycles toelemental metal sub-cycles in one or more super-cycles is less than one.In some embodiments the ratio of metal nitride deposition sub-cycles toelemental metal sub-cycles in one or more super-cycles is between about1 and about 3. In some embodiments the ratio of metal nitride depositionsub-cycles to elemental metal sub-cycles in one or more super-cycles isbetween about 1 and about 50, between about 3 and about 30 or betweenabout 5 and about 20. In some embodiments the ratio of metal nitridedeposition sub-cycles to elemental metal sub-cycles in one or moresuper-cycles is about 0.5, about 1, about 3, about 5, about 10, about20, about 40 or about 50.

In some embodiments the ratio of first metal nitride depositionsub-cycles to second elemental metal deposition sub-cycles is the samein all of the complete super-cycles performed in the process. In otherembodiments the specific ratio of first metal nitride depositionsub-cycles to second elemental metal deposition sub-cycles can be variedin different complete super-cycles. The specific ratios can be selectedby the skilled artisan to provide the desired amounts of M¹, nitrogenand M² in the film and thus to achieve a film with the desiredproperties.

Although referred to as the first metal nitride deposition sub-cycle andthe second elemental metal deposition sub-cycle, in some embodiments oneor more super-cycles begins with the elemental metal depositionsub-cycle, which is followed (after repeating a desired number of times)by the metal nitride deposition sub-cycle.

In some embodiments, the ultimate M¹ _(x)M² _(y)N_(z) film that isformed will comprise more of M¹ than M². In some embodiments, theultimate M¹ _(x)M² _(y)N_(z) film that is formed will comprise more ofM² than M¹. In some embodiments at least 30%, at least 50%, at least80%, at least 90%, at least 95%, at least 98%, at least 99% or at least99.5% of the metal in the M¹ _(x)M² _(y)N_(z) film is M². In someembodiments less than 70%, less than 40%, less than 30%, less than 20%,less than 5%, less than 3%, less than 1% or less than 0.5% of the metalin the M¹ _(x)M² _(y)N_(z) film is M².

In some embodiments the M¹-precursor comprises Ti, Ta, Nb, Mo or W. Insome embodiments the M¹ precursor is a halide, such as a chloride of Ti,Ta, Nb, Mo or W. In some embodiments the M¹-precursor is metal-organicprecursor.

In some embodiments the nitrogen-precursor can be selected from thegroup consisting of ammonia, N₂H₄, nitrogen atoms, nitrogen containingplasma or nitrogen radicals.

In some embodiments the M²-precursor comprises Mo or W. In someembodiments the M² precursor is a halide, such as a fluoride of Mo or W,like MoF_(x) or WF₆. In some embodiments the M²-precursor is ametal-organic precursor.

In some embodiments M¹ is different from M².

In some embodiments the second reactant can be selected from the groupconsisting of boranes or silanes, such as diborane or disilane.

In some embodiments a thermal ALD process is used for depositing a M¹_(x)M² _(y)N_(z) film and the N-precursor is ammonia or N₂H₄. In someembodiments a plasma ALD process is used and the N-precursor fordepositing a M¹ _(x)M² _(y)N_(z) film comprises nitrogen atoms, nitrogencontaining plasma or nitrogen radicals.

Specific process conditions and parameters are provided below fordeposition of exemplary Ti_(x)W_(y)N_(z) films. The process conditionsdescribed with respect to these processes can be applied to thedeposition of other M¹ _(x)M² _(y)N_(z) films.

In some embodiments the ratio of metal nitride sub-cycles to elementalmetal sub-cycles is selected to deposit a film that closes at very thinthicknesses, such as less than about 3 nm (where closed means that atomsof the underlying substrate are not detected at the outermost surfaceanymore, as determined, for example, by LEIS). In some embodiments theratio of sub-cycles is selected such that the film is electricallycontinuous i.e. conducts current at very thin thicknesses, such as lessthan about 3 nm, less than about 2 nm, less than about 1.5 nm or evenless than about 1.0 nm. In some embodiments the ratio of sub-cycles isselected such that the film is continuous as a layer, but may containsome non-continuous features, such as holes, in the continuous matrix atvery thin thicknesses, such as less than about 3 nm, less than about 2nm, less than about 1.5 nm or even less than about 1.0 nm. In someembodiments the ratio of sub-cycles is selected such that the film isnot closed and may not be continuous, but still acts as a diffusionbarrier at very thin thicknesses, such as less than about 3 nm, lessthan about 2 nm, less than about 1.5 nm or even less than about 1.0 nm.

In some embodiments a pulsing ratio of 5 or greater, 10 or greater or 20or greater, such as 20 to 30, is selected to deposit a film that closes,is electrically conductive, continuous as a layer, or acts as adiffusion barrier quickly, as explained above. In some embodiments apulsing ratio of about 20 is selected to deposit a film that closes atabout 2 nm thickness.

In some embodiments a M¹ _(x)M² _(y)N_(z) film is deposited with an RMSroughness below about 2 nm, below about 1.5 nm, below about 1.0 nm, oreven below about 0.7 nm, where the thickness is from about 20 to about50 nm. However, in some embodiments the RMS roughness is below about 0.5nm, below about 0.4 nm or even below about 0.3 nm for films with athickness of less than about 10 nm. RMS roughness can be measured, forexample, by x-ray reflectivity (XRR).

Ti_(x)W_(y)N_(z) Film Deposition by ALD

As mentioned above, an atomic layer deposition process may comprisemultiple super-cycles, where each super-cycle comprises at least one TiNsub-cycle and at least one W sub-cycle. In some embodiments, eachdeposition sub-cycle comprises alternately and sequentially contactingthe substrate with a metal precursor and second precursor. The ratio ofthe TiN and W sub-cycles can be varied to achieve the desiredcomposition, and the number of super-cycles can be selected to deposit atitanium nitride film of the desired thickness. The number of eachsub-cycle in a super-cycle is limited such that a mixed Ti_(x)W_(y)N_(z)film is formed, and distinct TiN and W layers are not visible. In someembodiments the maximum number of consecutive TiN sub-cycles in asuper-cycle is about 30 to about 60, about 30 to about 50 or about 40.In a process using TiCl₄ and NH₃, as described below, the maximum numberis about 40 in some embodiments. The maximum number of consecutive Wsub-cycles in a super-cycle is about 3 to about 10, about 3 to about 6,or about 5 in some embodiments.

The super-cycle can be written as:

a[b(titanium precursor+nitrogen reactant)+c(second reactant+tungstenprecursor)], where (titanium precursor+nitrogen reactant) represents aTiN sub-cycle and b is the number of TiN sub-cycles in each super-cycle,(second reactant+tungsten precursor) represents a tungsten sub-cycle andc is the number of W sub-cycles in each super-cycle and a is the numberof super-cycles. Although illustrated with the TiN sub-cycle comingfirst in the super-cycle, in some embodiments in one or moresuper-cycles the tungsten sub-cycle comes first. Thus in someembodiments the TiN sub-cycle can be considered the first sub-cycle andthe tungsten sub-cycle can be considered the second sub-cycle, while insome embodiments the tungsten sub-cycle can be considered the firstsub-cycle and the TiN sub-cycle can be considered the second sub-cycle.

In some embodiments the titanium precursor can be a titanium halide,such as TiCl₄. In some embodiments the titanium precursor can be ametal-organic precursor. In some embodiments the nitrogen reactant canbe selected from the group consisting of ammonia, N₂H₄, nitrogen atoms,nitrogen containing plasma and nitrogen radicals. In some embodimentsthe second reactant can be a borane or silane, such as diborane ordisilane. In some embodiments the tungsten reactant can be a tungstenhalide, such as WF₆.

In some embodiments a super-cycle can be written asa[b(TiCl₄+NH₃)+c(Si₂H₆+WF₆)], where b is the number of TiN sub-cycles ineach super-cycle, c is the number of W sub-cycles in each super-cycleand a is the number of super-cycles.

The ratio of TiN to W sub-cycles can thus be given as b:c (or TiN:W). Insome embodiments the ratio of sub-cycles is constant in each ALDsuper-cycle in the ALD process. In other embodiments the ratio ofsub-cycles may be changed in one or more super-cycle. Unless indicatedotherwise, when a ratio of sub-cycles is provided herein, it refers tothe ratio of sub-cycles in a one or more specific super-cycles, ratherthan the ratio of total sub-cycles in a complete ALD process comprisingmultiple super-cycles.

In some embodiments the first and second deposition sub-cycles areperformed at same reaction temperature. In some embodiments thedeposition temperature for one or both of the TiN and W sub-cycles isabout 100 to about 700° C., about 200 to about 500° C., about 250 toabout 400° C., or about 325 to about 375° C. In some embodiments boththe TiN and W sub-cycles are carried out at about 350° C.

In some embodiments, the first and second deposition sub-cycles areperformed in the same reactor.

The first and second deposition sub-cycles may be provided at a selectedratio to deposit a thin film with a desired composition and desiredproperties. For example, in some embodiments the ratio of the first, TiNdeposition sub-cycle to the second W deposition sub-cycle in one or moreALD super-cycles may be from about 0.1 to about 100, about 0.25 to about50 or about 0.5 to about 40. In some embodiments the ratio of TiNdeposition sub-cycles to W sub-cycles in one or more super-cycles isless than one. In some embodiments the ratio of TiN depositionsub-cycles to W sub-cycles in one or more super-cycles is between about1 and about 3. In some embodiments the ratio of TiN depositionsub-cycles to W sub-cycles in one or more super-cycles is between about1 and about 50, between about 3 and about 30 or between about 5 andabout 20. In some embodiments the ratio of TiN deposition sub-cycles toW sub-cycles in one or more super-cycles is about 0.5, about 1, about 3,about 5, about 10, about 20, about 40 or about 50.

As mentioned above, the ratio of sub-cycles can be selected to achieve adesired composition and desired film properties. For example, in someembodiments the ratio of TiN to W deposition sub-cycles is increased toincrease the density of the film, or decreased to decrease the densityof the deposited film.

In some embodiments the ratio of TiN to W deposition sub-cycles isincreased to increase the resistivity of the deposited film, ordecreased to decrease the resistivity.

In some embodiments, a smooth Ti_(x)W_(y)N_(z) film that does not have acolumnar grain structure is deposited. In some embodiments the ratio ofTiN deposition sub-cycles to W sub-cycles is selected to be less than orequal to one and a Ti_(x)W_(y)N_(z) film nanocrystalline film that doesnot have a columnar grain structure is formed. In some embodiments whena ratio of less than one is used, the Ti_(x)W_(y)N_(z) film may beessentially W_(y)N_(z) film, where the amount of Ti is approximately 0at-%.

In some embodiments, the ratio of TiN deposition sub-cycles to Wsub-cycles is selected to be between about 3 and about 20 in order todeposit a Ti_(x)W_(y)N_(z) film comprising a solid solution of (W,Ti)₂Nthat does not have a columnar grain structure.

In some embodiments, the ratio of TiN deposition sub-cycles to Wsub-cycles is selected to be greater than about 30 in order to deposit aTi_(x)W_(y)N_(z) film comprising a solid solution of (Ti,W)N that doesnot have a columnar grain structure.

In some embodiments the ratio of TiN sub-cycles to W sub-cycles isselected to deposit a film that closes at very thin thicknesses, such asless than about 3 nm. In some embodiments the ratio of sub-cycles isselected such that the film is electrically continuous i.e. conductscurrent at very thin thicknesses, such as less than about 3 nm, lessthan about 2 nm, less than about 1.5 nm or even less than about 1.0 nm.In some embodiments the ratio of sub-cycles is selected such that thefilm is continuous as a layer, but may contain some non-continuousfeatures, such as holes, in the continuous matrix at very thinthicknesses, such as less than about 3 nm, less than about 2 nm, lessthan about 1.5 nm or even less than about 1.0 nm. In some embodimentsthe ratio of sub-cycles is selected such that the film is not closed andmay not be continuous, but still acts as a diffusion barrier at verythin thicknesses, such as less than about 3 nm, less than about 2 nm,less than about 1.5 nm or even less than about 1.0 nm.

In some embodiments a pulsing ratio of 5 or greater, 10 or greater or 20or greater, such as 20 to 30, is selected to deposit a film that closes,is electrically conductive, continuous as a layer, or acts as adiffusion barrier quickly, as explained above. In some embodiments apulsing ratio of about 20 is selected to deposit a film that closes atabout 2 nm thickness.

In some embodiments the ratio of first TiN deposition sub-cycles tosecond W deposition sub-cycles is the same in all of the complete ALDsuper-cycles performed in the ALD process. In other embodiments thespecific ratio of first TiN deposition sub-cycles to second W depositionsub-cycles can be varied in different complete ALD super-cycles. Thespecific ratios can be selected by the skilled artisan to provide thedesired amounts of titanium, nitrogen and tungsten in the film and thusto achieve a film with the desired properties.

In some embodiments, the ultimate Ti_(x)W_(y)N_(z) film that is formedwill comprise more titanium than tungsten. In some embodiments at least30%, at least 50%, at least 80%, at least 90%, at least 95%, at least98%, at least 99% or at least 99.5% of the metal in the Ti_(x)W_(y)N_(z)film is tungsten. In some embodiments less than 70%, less than 40%, lessthan 30%, less than 20%, less than 5%, less than 3%, less than 1% orless than 0.5% of the metal in the Ti_(x)W_(y)N_(z) film is tungsten.

In some embodiments, as illustrated in FIG. 1, an ALD process forforming a Ti_(x)W_(y)N_(z) film on a substrate in a reaction chambercomprises multiple ALD super-cycles 100. Each super-cycle comprises afirst TiN deposition sub-cycle 200 and a second W deposition sub-cycle300. The super-cycle 100 is repeated as many times as desired to deposita Ti_(x)W_(y)N_(z) film of the desired thickness. The ratio of thesub-cycles 200, 300 within the super-cycle 100 may be selected toachieve a film with the desired composition and properties.

The first titanium nitride deposition sub-cycle comprises:

-   -   pulsing a vaporized first titanium precursor, such as TiCl₄ into        the reaction chamber 210 to form at most a molecular monolayer        of titanium precursor on the substrate,    -   purging the reaction chamber 220 to remove excess titanium        precursor and reaction by products, if any,    -   providing a pulse of a nitrogen reactant, such as NH₃, into the        reaction chamber 230, where the nitrogen source contacts and        reacts with the titanium precursor on the substrate to form        titanium nitride,    -   purging the reaction chamber 240 to remove excess nitrogen        source and any gaseous by-products formed in the reaction        between the titanium precursor layer on the first surface of the        substrate and the nitrogen reactant, and    -   repeating 250 the pulsing and purging steps.

In some embodiments, the first deposition sub-cycle is repeated 1, 2, 3,4, 5, 10, 20, 50, 100 or more times in succession. In some embodimentsthe first deposition sub-cycle is repeated no more than about 30-60times consecutively, up to about 30 to 50 times consecutively, or up toabout 40 times consecutively.

The atomic layer deposition super-cycle 100 for forming theTi_(x)W_(y)N_(z) film also comprises one or more second tungstendeposition sub-cycles 300. In some embodiments, the second tungstendeposition sub-cycle 300 comprises:

-   -   pulsing a vaporized tungsten precursor, such as WF₆ into the        reaction chamber 310 to form at most a molecular monolayer of        tungsten precursor on the substrate,    -   purging the reaction chamber 320 to remove excess tungsten        precursor and reaction by products, if any,    -   providing a pulse of a second reactant, such as Si₂H₆, into the        reaction chamber 330, where the second reactant reacts with the        tungsten precursor on the substrate to form elemental tungsten,    -   purging the reaction chamber 340 to remove excess second        reactant and any gaseous by-products formed in the reaction        between the tungsten precursor layer on the surface of the        substrate and the second reactant, and    -   repeating 350 the pulsing and purging steps.

In some embodiments, the second deposition sub-cycle 300 is repeated 1,2, 3, 4, 5, 10, 20, 50, 100 or more times in succession. In someembodiments the second deposition sub-cycle is repeated about 3 to 6times, or about 5 times.

Other methods for depositing tungsten are described in U.S. Pat. No.6,475,276, which is incorporated by reference herein.

The first and second deposition sub-cycles 200,300 are repeated multipletimes in a complete ALD super-cycle 100, and the complete ALDsuper-cycle 100 is repeated to form a Ti_(x)W_(y)N_(z) film of a desiredthickness comprising a desired concentration of titanium, nitrogen andtungsten.

In some embodiments, the number of times the first deposition sub-cycle200 and second deposition sub-cycle 300 are repeated is the same in eachcomplete ALD super-cycle 100. In other embodiments, the number of firstand second deposition sub-cycles 100, 200 varies in one or more completeALD super-cycles 100. The number of first and second sub-cycles 100, 200in each complete ALD super-cycle 100 and the total number of first andsecond sub-cycles 100, 200 and total ALD super-cycles 100 can beadjusted to achieve deposition of a Ti_(x)W_(y)N_(z) film of a desiredthickness and composition.

In some embodiments, each first and/or second deposition sub-cycle formsat most a monolayer of titanium nitride and tungsten respectively.

Although illustrated as beginning with the first deposition sub-cycle200, each complete ALD cycle may begin and end with either the first 100or second 200 deposition sub-cycle. For example, each ALD super-cyclefor forming the Ti_(x)W_(y)N_(z) film can be started with the firsttitanium nitride deposition sub-cycle or the tungsten depositionsub-cycle. In some embodiments one or more super-cycles may begin withthe tungsten sub-cycle.

In some embodiments the titanium reactant in the titanium nitridedeposition sub-cycle is a titanium halide, such as TiCl₄ and thenitrogen reactant is NH₃.

In some embodiments the tungsten reactant in the tungsten depositionsub-cycle is a tungsten halide, such as WF₆ and the second reactant is asilane or borane, such as Si₂H₆.

The precursors employed in the processes may be solid, liquid or gaseousmaterial under standard conditions (room temperature and atmosphericpressure), provided that the metal precursor is in vapor phase before itis conducted into the reaction chamber and contacted with the substratesurface. S

“Pulsing” a vaporized reactant onto the substrate means that the vaporis conducted into the chamber for a limited period of time. Typically,the pulsing time is from about 0.05 to 10 seconds. However, depending onthe substrate type and its surface area, the pulsing time may be evenhigher than 10 seconds.

As an example, for a 300 mm wafer in a single wafer ALD reactor, theprecursors are typically pulsed for from about 0.05 to 10 seconds, morepreferably for from about 0.1 to 5 seconds and most preferably for fromabout 0.3 to 3.0 seconds. However, pulsing times can be on the order ofminutes in some cases. The optimum pulsing time can be readilydetermined by the skilled artisan based on the particular circumstances.

The mass flow rate of the metal precursor can be determined by theskilled artisan. In some embodiments, for example for deposition on 300mm wafers, the flow rate of the reactants is preferably between about 1and 1000 sccm, about 10 to about 800 sccm, or about 50 to about 500sccm, without limitation.

The pulsing time and mass flow rate of each of the reactants can beselected independently. In some embodiments the pulsing time (and/ormass flow rates) of two or more of the reactants is the same, while insome embodiments the pulsing times (or mass flow rates) are different.

The pressure in the reaction chamber is typically from about 0.01 to 20mbar, more preferably from about 1 to about 10 mbar. However, in somecases the pressure will be higher or lower than this range, as can bereadily determined by the skilled artisan depending on multipleparameters, such as the particular reactor being used, the process andthe precursors.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature, as discussed above. Thepreferred deposition temperature may vary depending on a number offactors such as, and without limitation, the reactant precursors, thepressure, flow rate, the arrangement of the reactor, and the compositionof the substrate including the nature of the material to be depositedon. The specific growth temperature may be selected by the skilledartisan based on the particular circumstances.

The processing time depends, in part, on the thickness of the layer tobe produced, the composition of the film, and the growth rate of theindividual deposition sub-cycles and the overall growth rate.

In some embodiments the titanium nitride is deposited by ALD over asubstrate surface to form a conformal thin film of between about 1 nmand about 200 nm, between about 1 nm and about 50 nm in thickness,between about 1 nm and about 30 nm, and in some cases between about 2 nmand about 10 nm. In some embodiments the thickness of the metal nitridelayer is less than 10 nm, or less than 5 nm.

The present methods allow for the formation of completely closed layersat very low thicknesses. In some embodiments a metal nitride layer isformed that closes with a thickness of about 3 nm or less, or athickness of about 2 nm or less, as described above.

In an exemplary embodiment, an ALD sub-cycle for depositing titaniumnitride comprises alternatingly and sequentially contacting thesubstrate with a Ti precursor such as TiCl₄ and a nitrogen reactant suchas ammonia. An ALD sub-cycle for forming tungsten comprisesalternatingly and sequentially contacting the substrate with a tungstenprecursor, such as WF₆ and a second reactant such as Si₂H₆.

In some embodiments, the Ti_(x)W_(y)N_(z) film is deposited conformallyover vertical and horizontal surfaces.

In some embodiments a Ti_(x)W_(y)N_(z) film is deposited with an RMSroughness below about 2 nm, below about 1.5 nm, below about 1.0 nm, oreven below about 0.7 nm, where the thickness is from about 20 to about50 nm. However, in some embodiments the RMS roughness is below about 0.5nm, below about 0.4 nm or even below about 0.3 nm for films with athickness of less than about 10 nm. RMS roughness can be measured, forexample, by XRR.

In some embodiments a Ti_(x)W_(y)N_(z) film comprisingTi_(0.26)W_(0.33)N_(0.41) is deposited. Such a film may be deposited,for example, by utilizing a ratio of TiN to W sub-cycles of about 20:1.

In some embodiments a Ti_(x)W_(y)N_(z) film that does not have acolumnar grain structure is deposited.

In some embodiments, a Ti_(x)W_(y)N_(z) film with a nanocrystallinegrain size is deposited.

It will be apparent to the skilled artisan that the above describedprocesses and films will be beneficial at any of a number of integratedcircuit fabrication steps and will find use in a wide variety ofcontexts. In some embodiment, a Ti_(x)W_(y)N_(z) film deposited by themethods provided herein is used as a gate electrode, an electrode for amemory device, a phase-change memory, such as GST, a heater material, acapacitor electrode, such as a MIM, MIS or MIMIM electrode and the like,a diffusion barrier, such as a copper diffusion barrier or a contactplug.

Various modifications, omissions and additions may be made to themethods and structures described above without departing from the scopeof the invention. All such modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

Examples

Ti_(x)W_(y)N_(z) films were deposited by ALD in a Pulsar® 2000 R&Dreactor. The films were deposited with a super-cycle method using thefollowing basic binary chemistries for TiN and W:z[x(TiCl₄+NH₃)+y(Si₂H₆+WF₆)]. The reactor temperature was 350° C. Thesteady state flow rates for Si₂H₆ and WF₆ were 100 sccm, and 240 sccmfor NH₃. TiCl₄ was filled in the liquid source, which was in vapor pushmode at room temperature (21° C.) and used N₂ as the carrier gas.

The basic process parameters were: TiCl₄; 50 ms pulse/5 s purge, NH₃; 10s pulse/5 s purge, Si₂H₆; 0.5 pulse/5 s purge and WF₆; 0.5 s pulse/5 spurge.

The films were deposited on 200 mm, 20 nm TiN/20 nm SiO₂/Si and 20 nmSiO₂/Si wafers and on 2 nm HfO₂/Si planar wafer pieces (≈10×10 cm) or onpatterned native SiO₂/Si (≈5×5 cm) pieces for conformality. The pieceswere placed on 200 mm adapter wafers during the deposition runs. Filmcompositions were altered by changing the TiN/W cycle ratio (x/y) andfilm thicknesses were controlled by the number of super-cycles (z).

The films were characterized by four point probe measurements with CDEResmap 168 for sheet resistance, x-ray reflectivity (XRR) with Brüker D8Advance for thickness, roughness and density, by x-ray photoelectronspectroscopy (XPS) with PHI Quantum 2000 using monochromated AlK_(α) forcomposition (analysis done by EAG labs, East Windsor, N.J.), bysecondary electron microscope (SEM) with Hitachi S-4800 field emissionscanning electron microscope for morphology and conformality and byheated stage x-ray diffraction (XRD) with PANalytical X'Pert Pro MPDX-ray diffractometer with CuK_(α) radiation and HTK 1200 Anton Paar ovenin nitrogen and air atmospheres for crystallographic phase evolution asa function of annealing temperature.

Table 1 summarizes the composition, resistivity, roughness, density andgrowth rates of the TiN/W mixed process with different TiN/W cycleratios.

TABLE 1 Properties of the ALD Ti_(x)W_(y)N_(z) layers. The compositionsreported in the table are the compositions of the films measured by XPSafter sputtering with 2 keV Ar⁺ ions until the surface carboncontamination in the signals was absent. Layer Layer Layer N, O, F, Si,Ti, W, TiN/W TiN/(TiN + W) Roughness, nm Density, g/cm³ Resistivity, GR,Å/ at.- at.- at.- at.- at.- at.- cycle ratio cycle ratio (RMS, XRR)(XRR) μΩcm sub-cycle % % % % % % W 0 4.15 17.3 122.2 6.26 0.5 1.3 0.33.0 0.1 94.8 0.5 0.33 2.14 16.5 187.8 2.24 8.5 0.5 0.3 2.0 0.0 88.7 10.50 0.65 16.1 173.6 0.78 9.6 0.7 0.0 0.9 0.1 88.7 3 0.75 1.15 12.5622.3 0.77 21.0 0.6 3.0 1.0 3.1 71.4 5 0.83 1.96 11.9 711.4 0.63 25.70.4 3.0 1.2 7.2 62.4 20 0.95 1.01 8.6 553.7 0.33 39.9 0.3 2.3 0.5 24.932.0 40 0.98 0.65 7.8 381.6 0.30 44.0 0.6 1.6 0.8 32.2 20.8 TiN 1 2.745.3 143.1 0.24 53.2 0.8 0.0 0.2 45.7 0.0

Pure W films grew with a high growth rate of 6 Å/cycle, comparable tothe growth rates reported in the literature on Al₂O₃. However, theroughness of the W film was also very high. Adding some TiN cycles inbetween the W cycles decreased the growth rate of the films and at thesame time the roughness of the film was reduced substantially.Surprisingly though, the films did not contain any titanium when theTiN/W cycle ratio was ≦1. Instead, the resultant film was W_(x)N_(y)with less than 10 at-% nitrogen and some silicon impurity. This mayindicate that the TiN cycles in between the W cycles modified thenucleation behavior of W and resulted in lower growth rates and smootherfilms.

When the TiN/W cycle ratio was increased to ≧3, the films started toshow a further increase in nitrogen content and a slow increase intitanium content with an increasing TiN/W cycle ratio. This suggestedthat when an adequate amount of TiN cycles was done before the W cycle,the Si₂H₆ and WF₆ was not able to remove all the titanium from thesurface and therefore the titanium content of the films graduallystarted to increase.

The resistivity of the films first increased with increasing nitrogencontent when the titanium content of the film was low, and then startedto decrease again when the titanium content of the films was more than≈20 at-%.

The crystallographic phases of the films were studied by x-raydiffraction analysis. Pure W films showed β-W crystal structure. Thestabilization of the metastable β-W phase for the pure ALD tungsten hasnot been reported before. In order to determine whether the β-Wstabilization is a general result of the ALD W process itself, or if itwas stabilized by the HfO₂ substrate, the pure W process was also run onTiN and SiO₂ substrates. These results are presented in FIGS. 2A-C,which show XRD patterns of 100 cycles of pure ALD-W films deposited onTiN (FIG. 2A), SiO₂ (FIG. 2B) and HfO₂ (FIG. 2C) surfaces. The XRD peakshifts to higher 2θ-values indicate that the films have residual tensilestress in all cases. The peak intensity increase in FIG. 2A is causedmainly by the increased grain size with higher deposition temperatureand partly because of the higher growth rate with higher depositiontemperature. At 150° C. there were no film growth on the TiN surface

The TiN substrate was found to promote the stabilization of β-W crystalstructure, whereas on SiO₂ substrates the resultant film seemed to beα-W with small crystallite size, as indicated by the wide XRD 2θ peak at≈40°. In all cases, the XRD 2θ peaks were shifted to higher 2θ valuescompared to the powder diffraction reference values, indicating that thetungsten film had tensile residual stress on all the surfaces. However,the shift was greater for the β-W on TiN and HfO₂ than for the α-W onSiO₂. The α-W to β-W transition may also partly explain the higher ALDgrowth rates (≈6 Å/cycle) for W observed on TiN and HfO₂ and what hasalso been reported in the literature on Al₂O₃, compared to the growthrates reported on SiO₂ (≈3 Å/cycle). β-W has a lattice parameter of 5.05Å, whereas for α-W it is 3.16 Å.

FIGS. 3A and B show the results for deposition of mixed Ti_(x)W_(y)N_(z)films on HfO₂. With TiN/W cycle ratios of less than 3 the XRD analysisrevealed two very wide peaks at 40 and 70°. These peaks could not beassigned to any of the compounds containing W and N in the XRD database;however their position matches the β-W peaks, so it is possible thatthese films still have the crystal structure of β-W, but have anextremely small crystallite size.

The Ti_(x)W_(y)N_(z) films formed with TiN/W cycle ratios 3≦5 (Ticontent 3≦7 at-%) adapted the crystal structure of W₂N with tungstenatoms randomly displaced by titanium atoms in the lattice. For TiN/Wcycle ratios between 3 and 5, the W₂N peaks in the Ti_(x)W_(y)N_(z)films were visible, but with 2 theta values shifted in between the W₂Nand TiN peaks. Also the intensity ratios of the XRD peaks changed withthe composition of the Ti_(x)W_(y)N_(z) layer. This type of behavior inthe XRD pattern is typical for a solid solution.

With larger TiN/W cycle ratios the XRD peaks are shifted closer to theTiN peaks. In the case of the films deposited using TiN/W cycle ratios≧20 (Ti content≧25 at-%), the films adapt the crystal structure of TiNwith titanium atoms randomly displaced by tungsten atoms in the lattice.

Both W_(x)N_(y) and Ti_(x)W_(y)N_(z) films exhibited substantially widerXRD peaks than pure W or TiN films with comparable thicknesses. Thegrain size estimated with the Debye-Scherrer method was ≈2 nm forW_(0.9)N_(0.1) (1:1 TiN/W cycle ratio) and ≈20 nm forTi_(0.26)W_(0.33)N_(0.41) (20:1 TiN/W cycle ratio) film. FIG. 4 presentsa comparison of the morphology of the W_(x)N_(y) and Ti_(x)W_(y)N_(z)layers deposited at various TiN:W sub-cycle ratios, along with pure Wand TiN. The columnar grain structure clearly visible in pure W and TiNfilms is absent in the SEM images of the mixed process films. Thisconfirms that the smooth film surfaces modeled in the XRR analysis andthe wide peaks in the XRD patterns are a consequence of thenanocrystalline phase of the mixed process films with no visible grainmorphology in the SEM analysis.

FIG. 5 presents a SEM image of a W_(0.9)N_(0.1) (1:1 TiN/W cycle ratio)film in a 3D trench structure. The true ALD nature in the growth of thefilm is evident within the trench, showing constant film thicknessinside the trench even though the trench width increased with its depth.

The stability and oxidation resistance of the nanocrystalline phase of aternary Ti_(x)W_(y)N_(z) film with a composition ofTi_(0.26)W_(0.33)N_(0.41) (20:1 TiN/W cycle ratio) was studied by heatedstage XRD. In nitrogen atmosphere the nanocrystalline phase was stableat up to 875° C. with no sign of grain coarsening during the heatingcycles as shown in FIG. 6A. FIG. 6B shows a comparison with a pure TiNfilm with a similar thickness. FWHM was ≈0.7° forTi_(0.26)W_(0.33)N_(0.41) and ≈0.4° for TiN. This result suggests thatthe theoretically predicted high thermodynamic stability of thenanocrystalline phase in Ti—W alloys may be true also for the Ti—W—Nsystem. Grain size estimated with the Debye-Sherrer method was about 20nm for a 40 nm thick Ti_(0.26)W_(0.33)N_(0.41) film.

Results in an air atmosphere are presented in FIGS. 7A and B. TheTi_(0.26)W_(0.33)N_(0.41) film started to oxidize around 500° C., firstforming an amorphous oxide followed by the crystallization of WO₃ at675° C., crystallization of TiO₂ anatase starting at 750° C. and finallya phase change from TiO₂ anatase to TiO₂ rutile starting at 850° C. Theformation of an amorphous oxide in the beginning of the oxidationprocess is different from pure W or TiN oxidation, which oxidizedirectly to crystalline WO₃ or TiO₂. This is a further indication thatthe crystal size and structure of the Ti_(x)W_(y)N_(z) is such that itdoes not promote any long range ordering in the formed oxides.

LEIS analysis showed that at a TiN/W sub-cycle pulsing ratio of about20:1, the Ti_(x)W_(y)N_(z) film seems to close at about 2 nm thickness(FIGS. 8A and B). The percentage of Ti in the film also increases morerapidly at a pulsing ratio of 20:1 relative to lower ratios (FIGS. 9Aand B).

We claim:
 1. An atomic layer deposition (ALD) process for depositing ametal nitride film on a substrate, the process comprising a plurality ofsuper-cycles, each super-cycle comprising a TiN sub-cycle and a Wsub-cycle, wherein the TiN sub-cycle comprises alternately andsequentially contacting the substrate with a titanium precursor and anitrogen reactant; wherein the W sub-cycle comprises alternately andsequentially contacting the substrate with a tungsten precursor and asecond precursor, wherein the second precursor is a silane or borane;and wherein the film comprises a mixed metal nitride.
 2. The process ofclaim 1, wherein the titanium precursor is a titanium halide ormetal-organic titanium compound and the tungsten precursor is a tungstenhalide or metal-organic tungsten compound.
 3. The process of claim 2,wherein the titanium precursor is TiCl₄ and the tungsten precursor isWF₆.
 4. The process of claim 1, wherein the nitrogen reactant isselected from the group consisting of ammonia, N₂H₄, nitrogen atoms,nitrogen containing plasma and nitrogen radicals.
 5. The process ofclaim 1, wherein the second precursor comprises disilane or trisilane.6. The process of claim 1, wherein the TiN sub-cycle and the W sub-cycleare carried out at a ratio of at least about 3 in at least one of theplurality of super-cycles.
 7. The method of claim 1, wherein the filmforms a continuous layer.
 8. A method for forming a film comprising amixed metal nitride on a substrate in a reaction chamber, the methodcomprising: conducting an atomic layer deposition super-cycle comprisinga metal nitride sub-cycle and an elemental metal sub-cycle, wherein thefirst metal nitride sub-cycle comprises: pulsing a first vapor-phasemetal precursor comprising a first metal (M¹) into the reaction chamberto form at most a molecular monolayer of the metal precursor on thesubstrate; and pulsing a vapor phase nitrogen reactant into the reactionchamber, where the nitrogen reactant reacts with the metal precursor onthe substrate to form a metal nitride; and wherein the second elementalmetal sub-cycle comprises: pulsing a second vapor phase metal precursorcomprising a second different metal (M²) into the reaction chamber toform at most a molecular monolayer of second metal precursor on thesubstrate; and pulsing a vapor phase second reactant into the reactionchamber that reacts with the second metal precursor to form elementalmetal; and repeating the atomic layer deposition super-cycle to form aternary metal nitride film of the desired thickness, the ternary metalnitride film having the formula M¹ _(x)M² _(y)N_(z), wherein x is from 0to 1.5, y is from 0.05 to 4 and z is from 0 to 2, and wherein eachsuper-cycle comprises up to ten repetitions of the second elementalmetal sub-cycle, and wherein a ratio of the first metal nitridesub-cycle to the second elemental metal sub-cycle in each super-cycle is0.5 to
 40. 9. The method of claim 8, wherein M¹ is selected from Ti, Ta,Nb, Mo and W and M² is selected from Mo and W.
 10. The method of claim8, wherein the first metal precursor comprises a metal halide ormetal-organic compound.
 11. The method of claim 8, wherein the secondmetal precursor comprises a metal halide or metal-organic compound. 12.The method of claim 8, wherein the second reactant comprises a silane orborane.
 13. The method of claim 8, wherein the nitrogen reactantcomprises ammonia, N₂H₄, nitrogen atoms, nitrogen containing plasma ornitrogen radicals.
 14. The method of claim 8, wherein the metal nitridefilm does not have a columnar grain structure.
 15. A method for forminga film comprising a mixed metal nitride on a substrate in a reactionchamber, the method comprising: a first metal nitride sub-cyclecomprising: contacting the substrate with a first vapor-phase metalprecursor comprising a first metal to form at most a molecular monolayerof the metal precursor on the substrate; and contacting the substratewith a vapor phase nitrogen reactant, such that the nitrogen reactantreacts with the metal precursor on the substrate to form a metalnitride; and a second elemental metal sub-cycle comprising: contactingthe substrate with a second vapor phase metal precursor comprising asecond metal different from the first metal to form at most a molecularmonolayer of second metal precursor on the substrate; and contacting thesubstrate with a vapor phase second reactant that reacts with the secondmetal precursor to form elemental metal; and repeating the first andsecond sub-cycles to form a ternary metal nitride film of a desiredthickness, wherein the ternary metal nitride film has a roughness ofless than 2 nm as measured by x-ray reflectivity.
 16. The method ofclaim 15, wherein the second elemental metal sub-cycle is performedbefore the first metal nitride sub-cycle.
 17. The method of claim 15,wherein the first metal is selected from Ti, Ta, Nb, Mo and W and thesecond metal is selected from Mo and W.
 18. The method of claim 15,wherein the second reactant comprises a silane or borane.
 19. The methodof claim 15, wherein the first sub-cycle and second sub-cycle arerepeated at a selected ratio in a plurality of super-cycles.
 20. Themethod of claim 19, wherein the first sub-cycle is repeated no more thanabout 40 times consecutively and the second sub-cycle is repeated nomore than about 10 times consecutively in each of the plurality ofsuper-cycles.
 21. The method of claim 15, wherein the roughness of lessthan about 2 nm is at a film thickness of about 20 to about 50 nm.